We first introduce a partition of unity. Following the construction given in [1]}, we have the following partition of unity. For two constants \(c_{1}\)  and \(c_{2}\)  such that \(\frac{\sqrt{3}}{2}<c_{1}<c_{2}<1\)  , we have a family of functions \(\alpha _l\in C_c^{\infty }(R^3), l\in Z^3\)  such that
\(\sum \limits _{l\in Z^3}\alpha _l^2=1,\quad \hbox{supp}\alpha _l\subseteq B_{c_2}(l).\) 
